Crude oil originates from the decomposition and transformation of aquatic, mainly marine, living organisms and/or land plants that became buried under successive layers of mud and silt some 15-500 million years ago. They are essentially very complex mixtures of many thousands of different hydrocarbons. Depending on the source, the oil predominantly contains various proportions of straight and branched-chain paraffins, cycloparaffins, and naphthenic, aromatic, and polynuclear aromatic hydrocarbons. These hydrocarbons can be gaseous, liquid, or solid under normal conditions of temperature and pressure, depending on the number and arrangement of carbon atoms in the molecules.
Crude oils vary widely in their physical and chemical properties from one geographical region to another and from field to field. Crude oils are usually classified into three groups according to the nature of the hydrocarbons they contain: paraffinic, naphthenic, asphaltic, and their mixtures. The differences are due to the different proportions of the various molecular types and sizes. One crude oil can contain mostly paraffins, another mostly naphthenes. Whether paraffinic or naphthenic, one can contain a large quantity of lighter hydrocarbons and be mobile or contain dissolved gases; another can consist mainly of heavier hydrocarbons and be highly viscous, with little or no dissolved gas. Crude oils can also include heteroatoms containing sulfur, nitrogen, nickel, vanadium and other elements in quantities that impact the refinery processing of the crude oil fractions. Light crude oils or condensates can contain sulfur in concentrations as low as 0.01 W %; in contrast, heavy crude oils can contain as much as 5-6 W %. Similarly, the nitrogen content of crude oils can range from 0.001-1.0 W %.
The nature of the crude oil governs, to a certain extent, the nature of the products that can be manufactured from it and their suitability for special applications. A naphthenic crude oil will be more suitable for the production of asphaltic bitumen, a paraffinic crude oil for wax. A naphthenic crude oil, and even more so an aromatic one, will yield lubricating oils with viscosities that are sensitive to temperature. However, with modern refining methods there is greater flexibility in the use of various crude oils to produce many desired type of products.
Common crude oil fractions and their nominal boiling points are given in Table 1.
TABLE 1FractionBoiling Point, ° C.Methane−161.5 Ethane−88.6Propane−42.1Butanes −6.0Light Naphtha36-90Mid Naphtha 90-160Heavy Naphtha160-205Light gas Oil205-260Mid Gas Oil260-315Heavy gas Oil315-370Light Vacuum Gas Oil370-430Mid Vacuum Gas Oil430-480Heavy vacuum gas oil480-565Vacuum Residue565+ 
Exhausted oil fields may still contain low concentrations of oil known as residual oil. Residual oil can also be found naturally in fields not previously worked. Residual oil is often mixed with water, and it cannot be recovered conventional techniques. While residual oil fractions that boil above 350° C. contain heavy polynuclear aromatic hydrocarbons, they can nevertheless be converted into valuable products by processing techniques such as delayed coking, hydroprocessing, gasification, solvent deasphalting, and fluid catalytic cracking. For example, delayed coking technology is used to process heavy residual oils to reject carbon as a coke and to recover light fractions as a result of cracking paraffinic side chains and naphthenic rings. The carbon produced in delayed coking technology has three grades: fuel, anode, and needle grades.
Traditionally, the values of products recovered from delayed coking, including coke, gas, and distillates, could only be determined after processing. Due to the processing required and the number of analyses involved, the delayed coking and assay work-up is both costly and time consuming.
This invention discloses a system and method in which the assay values of the coke, gas, and distillates that could be derived from residual oils is actually calculated directly from the residual oil, without first requiring delayed coking or other processing. The invention will help producers, refiners, and marketers to benchmark the quality of the products and, as a result, valuate the products without first going thru costly and time consuming processing and oil assays. Whereas a conventional delayed coking processing and assay could take up to two months, this invention provides results within one hour.